JP2009121337A - Piston engine and stirling engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain durability deterioration of a piston and a cylinder by constraining foreign substances from entering a portion between the piston and the cylinder in a structure in which a gas bearing is interposed between the piston and the cylinder. <P>SOLUTION: A gas bearing GB is formed between the piston 20 and the cylinder 30. The gas bearing GB is formed between a piston diameter varying portion GT1 on a top face side of the piston 20 and a piston diameter varying portion GT2 on the side opposite to the top face side of the piston 20. An annular member 40T on the top face side and an annular member 40B on the side opposite to the top face side are fitted on the piston diameter varying portion GT1 on the top face side of the piston 20 and the piston diameter varying portion GT2 on the side opposite to the top face side of the piston 20, respectively. The annular member 40T on the top face side and the annular member 40B on the side opposite to the top side are made up of a material with lower hardness than that of an inner surface 30S of the cylinder 30. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a piston engine and a Stirling engine in which a piston reciprocates in a cylinder without using a piston ring or lubricating oil.

  In recent years, Stirling engines with excellent theoretical thermal efficiency have attracted attention in order to recover exhaust heat and factory exhaust heat of internal combustion engines mounted on vehicles such as passenger cars, buses, and trucks. Patent Document 1 discloses a Stirling engine in which a gas bearing is interposed between a piston and a cylinder. Patent Document 2 discloses a pilot-type solenoid valve having a structure in which a piston ring provided on a piston is brought into contact with a cylinder so that foreign matter bitten between the piston ring and the inner wall of the cylinder is easily blown away.

JP 2006-183666 A JP-A-6-235478

  By the way, when a gas bearing is interposed between the piston and the cylinder as in the Stirling engine disclosed in Patent Document 1, if a minute foreign matter is mixed in the working fluid, the foreign matter is inserted between the piston and the cylinder. May get in. As a result, the durability of the piston or cylinder may be reduced. Moreover, since the piston ring disclosed in Patent Document 2 contacts the inner wall of the cylinder and blows off foreign matter, this is applied to the structure disclosed in Patent Document 1 that includes a gas bearing between the piston and the cylinder. I can't.

  Thus, in the structure in which the gas bearing is interposed between the piston and the cylinder, there is room for improvement in order to suppress the entry of foreign matter between the piston and the cylinder. The present invention has been made in view of the above, and in a structure in which a gas bearing is interposed between a piston and a cylinder, the intrusion of foreign matter between the piston and the cylinder is suppressed, and The purpose is to suppress a decrease in durability.

  In order to achieve the above-mentioned object, a piston engine according to the present invention includes a piston that reciprocates in a cylinder, a gas bearing formed between the piston and the cylinder, and a reciprocating motion direction of the piston. And an annular member having a lower hardness than the inner surface of the cylinder, which is provided at at least one end of a region where the gas bearing is formed. With such a configuration, the piston engine according to the present invention captures and captures the foreign material entering the space between the piston and the cylinder by biting into the annular member. Thereby, the piston engine according to the present invention can suppress the intrusion of foreign matter between the piston and the cylinder, and can suppress the deterioration of the durability of the piston and the cylinder.

  As a preferred aspect of the present invention, in the piston engine, the piston is surrounded by an outer shell of the piston, and is provided with a plurality of gas reservoirs for accumulating gas and a plurality of side portions of the piston. It is desirable to have an air supply hole for allowing the gas to flow out between the piston and the cylinder to form the gas bearing.

  As a preferred aspect of the present invention, in the piston engine, the annular member is desirably provided at least on the top surface side of the piston.

  As a preferred aspect of the present invention, in the piston engine, the piston has a diameter of a predetermined portion from the top surface of the piston toward the end opposite to the top surface, than a diameter of a portion where the gas bearing is formed. The annular member has a clearance enlarged portion formed so as to have a clearance between the cylinder and the piston larger than a portion where the gas bearing is formed, and the annular member is formed on the piston on the top surface side of the piston. It is desirable to be provided in a portion where the diameter of the material changes.

  As a preferred aspect of the present invention, in the piston engine, it is desirable that the outer peripheral surface of the annular member is the same as the side surface of the piston or closer to the inner surface side of the cylinder than the side surface of the piston.

  As a preferred aspect of the present invention, in the piston engine, the annular member is an end member having a joint, and the free-form diameter is preferably larger than the inner diameter of the cylinder.

  As a preferred aspect of the present invention, in the piston engine, the annular member is disposed on an outer peripheral surface of the annular member in a direction crossing a direction in which the piston reciprocates and in a direction in which the piston reciprocates. It is desirable to provide a groove penetrating the end portions of each other.

  In order to achieve the above-described object, a Stirling engine according to the present invention includes a heater that heats a working fluid, a regenerator that is connected to the heater and through which the working fluid passes, and is connected to the regenerator. A heat exchanger including a cooler for cooling the working fluid, a cylinder into which the working fluid that has passed through the heat exchanger flows in and out, a piston that reciprocates in the cylinder, and the piston A gas bearing formed between the cylinder and an annular member having a lower hardness than the inner surface of the cylinder, provided at at least one end of a region where the gas bearing is formed in the reciprocating direction of the piston. And an approximate linear mechanism that supports the piston and moves the piston approximately linearly. With such a configuration, the Stirling engine according to the present invention captures and captures the foreign material entering the space between the piston and the cylinder by biting into the annular member. Thereby, the Stirling engine according to the present invention can suppress the intrusion of foreign matter between the piston and the cylinder, and can suppress the deterioration of the durability of the piston and the cylinder.

  According to the present invention, in a structure in which a gas bearing is interposed between a piston and a cylinder, intrusion of foreign matter between the piston and the cylinder can be suppressed, and a decrease in durability of the piston or the cylinder can be suppressed.

  Hereinafter, the present invention will be described in detail with reference to the drawings. The present invention is not limited by the best mode for carrying out the invention (hereinafter referred to as an embodiment). In addition, constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those in a so-called equivalent range. In the following, a Stirling engine is taken as an example of a piston engine, but the piston engine is not limited to this. Moreover, although the example which collect | recovers exhaust heat of the internal combustion engine mounted in a vehicle etc. using the Stirling engine which is a piston engine is demonstrated, the collection | recovery object of exhaust heat is not restricted to an internal combustion engine. For example, the present invention can also be applied to recovering waste heat from a factory, plant, or power generation facility.

  In the piston engine according to the present embodiment, a gas bearing is interposed between the piston and the cylinder, and at least one end of a region where the gas bearing is formed in the reciprocating direction of the piston is lower in hardness than the cylinder. It is characterized in that an annular member is provided. In the present embodiment, the gas bearing may be either a static pressure gas bearing or a dynamic pressure gas bearing.

  FIG. 1 is a cross-sectional view showing a configuration of a Stirling engine that is a piston engine according to the present embodiment. FIG. 2 is a plan view showing a gas bearing provided in the Stirling engine according to the present embodiment. FIG. 3A is an explanatory diagram illustrating a configuration example of a gas bearing provided in the Stirling engine according to the present embodiment and a support structure of a piston. 3-2 is explanatory drawing which shows the structural example of the gas bearing with which the Stirling engine which concerns on the modification of this embodiment is provided, and the support structure of a piston.

  The piston engine according to this embodiment is a heat engine, more specifically, a Stirling engine 100 that is an external combustion engine. The Stirling engine 100 is a so-called α-type in-line two-cylinder Stirling engine. In the present embodiment, the Stirling engine 100 functions as, for example, an exhaust heat recovery engine that recovers thermal energy from exhaust gas Ex of the internal combustion engine and extracts it as kinetic energy. The heat exchanger 108 of the Stirling engine 100 is disposed in the heater case 3 that functions as a passage through which the exhaust gas Ex of the internal combustion engine passes, and the Stirling engine 100 recovers thermal energy from the exhaust gas Ex of the internal combustion engine.

  In the Stirling engine 100, a high temperature side piston 20H housed in the high temperature side cylinder 30H and a low temperature side piston 20L housed in the low temperature side cylinder 30L are arranged in series. Hereinafter, the high temperature side cylinder 30H and the low temperature side cylinder 30L are referred to as the cylinder 30 when not distinguished from each other, and the high temperature side piston 20H and the low temperature side piston 20L are referred to as piston 20 when not distinguished from each other.

  The high temperature side cylinder 30 </ b> H and the low temperature side cylinder 30 </ b> L are supported or fixed directly or indirectly on the substrate 111 which is a reference body. In the present embodiment, the substrate 111 serves as a position reference for each component of the Stirling engine 100. Further, as will be described later, the Stirling engine 100 according to the present embodiment interposes the gas bearing GB between the high temperature side cylinder 30H and the high temperature side piston 20H and between the low temperature side cylinder 30L and the low temperature side piston 20L. .

  The Stirling engine 100 can hold the clearance between the piston 20 and the cylinder 30 with high accuracy by directly or indirectly attaching the high temperature side cylinder 30H and the low temperature side cylinder 30L to the substrate 111 which is a reference body. Thereby, the function of the gas bearing GB can be sufficiently exhibited. Further, the Stirling engine 100 can be easily assembled.

  Between the high temperature side cylinder 30H and the low temperature side cylinder 30L, a heat exchanger 108 including a substantially U-shaped heater (heater) 105, a regenerator 106, and a cooler 107 is provided. The inside of the heater 105, the regenerator 106, and the cooler 107 is filled with the working fluid of the Stirling engine 100. When the Stirling engine 100 is operated, the working fluid flows inside the heater 105, the regenerator 106, and the cooler 107.

  One end of the heater 105 constituting the heat exchanger 108 is disposed on the high temperature side cylinder 30H side, and the other end is disposed on the regenerator 106 side. The heater 105 heats the internal working fluid with heat energy of the exhaust gas Ex of the internal combustion engine. One end of the regenerator 106 is disposed on the heater 105 side, and the other end is disposed on the cooler 107 side, and the working fluid flowing from the heater 105 or the cooler 107 passes therethrough. One end of the cooler 107 is disposed on the regenerator 106 side, and the other end is disposed on the low temperature side cylinder 30L side. The cooler 107 cools the working fluid. The working fluid that has passed through the heat exchanger 108 flows into and out of the high temperature side cylinder 30H and the low temperature side cylinder 30L.

  The high temperature side cylinder 30H, the low temperature side cylinder 30L, and the heat exchanger 108 are filled with a working fluid (in this embodiment, air), and a Stirling cycle is configured by the thermal energy supplied from the heater 105 to the working fluid. The Stirling engine 100 is driven. The reciprocating motion of the high temperature side piston 20H and the low temperature side piston 20L is transmitted to the crankshaft 110, which is the output shaft, by the connecting rod 61, where it is converted into rotational motion. The space filled with the working fluid of the high temperature side cylinder 30H is called the high temperature side working fluid space MSH, and the space filled with the working fluid of the low temperature side cylinder 30L is called the low temperature side working fluid space MSL. This is simply referred to as working fluid space MS.

  Here, for example, the heater 105 and the cooler 107 can be configured by bundling a plurality of tubes made of a material having high thermal conductivity and excellent heat resistance. The cooler 107 may be air-cooled or water-cooled. Moreover, the regenerator 106 can be comprised with a porous heat storage body. Note that the configurations of the heater 105, the cooler 107, and the regenerator 106 are not limited to this example, and a suitable configuration can be selected depending on the heat conditions of the exhaust heat recovery target, the specifications of the Stirling engine 100, and the like.

  The high temperature side piston 20H and the low temperature side piston 20L are respectively supported inside the high temperature side cylinder 30H and the low temperature side cylinder 30L via gas bearings GB. That is, the piston 20 is supported in the cylinder 30 without using a piston ring and without using lubricating oil. Thereby, the friction between the piston 20 and the cylinder 30 can be reduced, and the efficiency of the Stirling engine 100 can be improved. Further, by reducing the friction between the piston 20 and the cylinder 30, the Stirling engine 100 is used under low quality and low temperature operating conditions, for example, when recovering the heat energy of the exhaust heat of the internal combustion engine. Even in this case, the Stirling engine 100 can recover the thermal energy from the exhaust heat.

  In order to constitute the gas bearing GB, as shown in FIG. 2, there is a predetermined gap between the piston 20 (high temperature side piston 20H, low temperature side piston 20L) and the cylinder 30 (high temperature side cylinder 30H, low temperature side cylinder 30L). A clearance tc is provided. The clearance tc is 10 μm to several tens of μm over the entire circumference of the piston 20. Here, the clearance tc shown in FIG. 2 is one clearance in the cross section when the piston 20 is cut along a plane including the axis of the piston 20. Therefore, when the diameter of the piston 20 in the region where the gas bearing GB is formed is DPg and the inner diameter of the cylinder 30 is DCg, DCg = DPg + 2 × tc.

  Here, since the gas bearing GB has a low ability (load ability) to withstand the force of the piston 20 in the diameter direction (lateral direction, thrust direction), it is preferable that the side force Fs of the piston 20 is substantially zero. For this reason, it is necessary to increase the linear motion accuracy of the piston 20 with respect to the axis (center axis) of the cylinder 30. In order to realize this, as shown in FIG. 3A, in the present embodiment, the high temperature side piston 20H and the low temperature side piston 20L are supported by an approximate linear mechanism 60 such as a grasshopper mechanism.

  The approximate linear mechanism 60 has a first arm 62 whose one end is rotatably attached to the casing 100C of the Stirling engine 100, and a second arm whose one end is rotatably attached to the casing 100C of the Stirling engine 100. 63, and a third arm 64 having one end rotatably connected to the end of the connecting rod 61 and the other end rotatably connected to the other end of the second arm 63. The connecting rod 61 is rotatably connected to the end of the third arm 64 at an end different from the end that is rotatably attached to the crankshaft 110. Further, the other end of the first arm 62 is rotatably connected between both ends of the third arm 63.

  If the approximate linear mechanism 60 comprised in this way is used, the high temperature side piston 20H and the low temperature side piston 20L can be reciprocated substantially linearly. As a result, the side force Fs of the high temperature side piston 20H and the low temperature side piston 20L becomes almost zero, so that the piston 20 can be sufficiently supported even by the gas bearing GB having a small load capacity. The approximate linear mechanism that supports the piston 20 is not limited to the grasshopper mechanism, and a watt link or the like may be used.

  Note that the grasshopper mechanism has an advantage that the entire Stirling engine 100 can be made compact because the size of the mechanism required to obtain the same linear motion accuracy is small compared to other linear approximation mechanisms. In particular, the Stirling engine 100 according to this embodiment is used for exhaust heat recovery of an internal combustion engine mounted on a vehicle, and the heat exchanger 108 is disposed in the exhaust gas passage of the internal combustion engine. If the Stirling engine 100 is entirely compact, the degree of freedom of installation is improved. Further, the approximate linear mechanism 60 is advantageous in that the thermal efficiency is improved because the mass of the mechanism necessary for obtaining the same linear motion accuracy is lighter than other mechanisms. Further, the approximate linear mechanism 60 has an advantage that the structure of the mechanism is relatively simple, so that it can be easily manufactured and assembled, and the manufacturing cost can be reduced.

  As shown in FIG. 1, components such as the high temperature side cylinder 30H, the high temperature side piston 20H, the connecting rod 61, and the crankshaft 110 that constitute the Stirling engine 100 are stored in a housing 100C. The casing 100C of the Stirling engine 100 includes a crankcase 114A and a cylinder block 114B. The space (crankcase internal space) CS in the crankcase 114A constituting the housing 100C is filled with gas. In the present embodiment, the gas is the same as the working fluid of the Stirling engine 100. The gas filled in the crankcase internal space CS is pressurized by a pump 115 which is a pressure adjusting means. The pump 115 may be driven by, for example, an internal combustion engine that is an exhaust heat recovery target of the Stirling engine 100, or may be driven using a driving unit such as an electric motor.

  In the Stirling engine 100, when the temperature difference between the heater 105 and the cooler 107 is the same, the higher the average pressure of the working fluid, the larger the pressure difference between the high temperature side and the low temperature side, so that a higher output can be obtained. The Stirling engine 100 according to the present embodiment pressurizes the gas filled in the crankcase inner space CS, thereby holding the working fluid in the working fluid space MS at a high pressure and generating more output from the Stirling engine 100. It is configured to be taken out. As a result, even when only a low-quality heat source can be used, such as exhaust heat recovery, more output can be extracted from the Stirling engine 100. Here, the output of the Stirling engine 100 increases substantially in proportion to the pressure of the gas filled in the housing 100C.

  In the Stirling engine 100 according to the present embodiment, a seal bearing 116 is attached to the housing 100C, and the crankshaft 110 is supported by the seal bearing 116. The Stirling engine 100 according to the present embodiment pressurizes the gas filled in the housing 100C, but the seal bearing 116 can minimize the leakage of the gas filled in the housing 100C. The output of the crankshaft 110 is taken out of the housing 100C via a flexible coupling 118 such as an Oldham coupling.

  As shown in FIGS. 1 and 3-1, the piston 20 included in the Stirling engine 100 has a top portion 20Tp, a side portion 20Sp, and a bottom portion 20Bp as outer shells, and a top portion 20Tp, a side portion 20Sp, and a bottom portion 20Bp. A space surrounded by a gas reservoir (hereinafter referred to as a pressure accumulation space) 20I. The outer shell of the piston 20 includes at least a top portion 20Tp, a side portion 20Sp, and a bottom portion 20Bp or a member corresponding to the bottom portion 20Bp. A gas introduction passage 21 communicating with the pressure accumulation space 20I is provided at the top portion 20Tp of the piston 20. The working fluid FL in the working fluid space MS is introduced into the pressure accumulation space 20I of the piston 20 through the gas introduction passage 21.

  A check valve 25 is provided on the pressure accumulation space 20I side of the top portion 20Tp of the piston 20 as a pressurizing state holding means in order to prevent a back flow of the working fluid FL introduced into the pressure accumulation space 20I. The check valve 25 is disposed inside the pressure accumulating space 20I, introduces the working fluid FL in the working fluid space MS from the gas introduction passage 21 to the pressure accumulating space 20I, and the working fluid FL in the pressure accumulating space 20I is the working fluid. Backflow into the space MS is prevented.

  The movement of the piston 20 increases the pressure (working fluid space pressure) Pms of the working fluid FL existing in the working fluid space MS in the cylinder 30 shown in FIG. When the valve opening pressure Po is exceeded, the check valve 25 is opened. Then, the working fluid FL in the working fluid space MS flows into the pressure accumulating space 20I through the gas introduction passage 21. Here, the valve opening pressure Po is set to a predetermined pressure higher than the pressure in the pressure accumulation space 20I (pressure in the pressure accumulation space) Pp.

  When the pressure Pms in the working fluid space decreases due to the movement of the piston 20 and becomes lower than the valve opening pressure Po, the check valve 25 is closed. This prevents the working fluid FL in the pressure accumulating space 20I from flowing back to the working fluid space MS. Thus, the check valve 25 has a pressurized state holding function for holding the pressurized state in the pressure accumulation space 20I and also has a working fluid introduction function for introducing the working fluid FL into the pressure accumulation space 20I. The working fluid FL introduced from the working fluid space MS to the pressure accumulating space 20I of the piston 20 passes through the plurality of air supply holes 22 provided in the side portion 20Sp of the piston 20 and the inner surface 30S of the cylinder 30. It flows out to clearance tc between. Thus, a gas bearing GB is formed between the piston 20 and the inner surface 30S of the cylinder 30. In addition, although the gas bearing GB is a static pressure gas bearing, the gas bearing applicable to this embodiment is not limited to this, A dynamic pressure gas bearing may be sufficient.

  Thus, during operation of the Stirling engine 100 shown in FIG. 1, the working fluid FL in the working fluid space MS is compressed as the piston 20 rises. When the working fluid space pressure Pms becomes higher than the valve opening pressure of the check valve 25, the check valve 25 opens. A part of the working fluid FL in the working fluid space MS is introduced into the pressure accumulating space 20I through the gas introduction passage 21. A part of the working fluid FL introduced into the pressure accumulating space 20I flows out into the clearance tc between the piston 20 and the cylinder 30 through a plurality of air supply holes 22 provided in the circumferential direction of the piston 20, and gas A bearing GB is formed.

  In this way, the working fluid FL introduced into the pressure accumulation space 20I of the piston 20 flows out between the piston 20 and the cylinder 30 to form the gas bearing GB, and as in the Stirling engine 100a shown in FIG. The working fluid FL may be supplied to the pressure accumulating space 20I of the piston 20 from the gas bearing pump 120, which is a gas bearing pressure generating means, disposed outside the housing 100C via the gas supply passage 45. Then, the working fluid FL introduced into the pressure accumulation space 20I may flow out from the air supply hole 22 to the clearance tc between the piston 20 and the cylinder 30 to form the gas bearing GB.

  The Stirling engine 100 has a complicated working fluid passage in the heat exchanger 108 in particular, and it is not always possible to completely remove foreign matters such as fine dust and dirt in the assembly process of the Stirling engine 100. Further, foreign matter may be released from the heater 105 or the like of the heat exchanger 108 after a long time operation. For this reason, foreign substances may be mixed in the working fluid FL of the Stirling engine 100.

  As described above, the Stirling engine 100 forms the gas bearing GB in the minute clearance tc formed between the piston 20 and the cylinder 30, thereby supporting the piston 20 in the cylinder 30. For this reason, there is a possibility that minute foreign matter mixed in the working fluid FL may enter a minute clearance tc formed between the piston 20 and the cylinder 30. If foreign matter enters the clearance tc, the surface of the piston 20 or the cylinder 30 may be affected to reduce the durability thereof, or the sliding resistance between the piston 20 and the cylinder 30 may be increased. Therefore, the Stirling engine 100 suppresses entry of foreign matter into the clearance tc between the piston 20 and the cylinder 30 with the configuration described below.

  FIG. 4 is an enlarged view of a piston and a cylinder included in the Stirling engine according to the present embodiment. FIG. 5 is a perspective view of an annular member provided on the piston of the Stirling engine according to the present embodiment, and FIG. 6 is a plan view of the annular member provided on the piston of the Stirling engine according to the present embodiment. FIG. 7 is an enlarged view of a portion where an annular member is attached to a piston included in the Stirling engine according to the present embodiment.

  In the present embodiment, an annular member (hereinafter referred to as an annular member) 40 having a lower hardness than the inner surface 30S of the cylinder 30 is provided at at least one end of a region where the gas bearing GB is formed in the reciprocating direction of the piston 20. . Then, the annular member 40 removes foreign matter that is to enter the clearance tc between the piston 20 and the cylinder 30 where the gas bearing GB is formed. As a result, entry of foreign matter into the clearance tc between the piston 20 and the cylinder 30 is suppressed.

  As shown in FIG. 4, the connecting portion between the top surface 20T of the piston 20 (hereinafter referred to as the piston top surface) and the side surface 20S is an end portion on the opposite side of the piston top surface 20T from the connecting portion (the end opposite to the top surface). It is formed in a step shape so that the diameter DP1 on the piston top surface 20T side is smaller than the diameter DP2 on the side surface 20S on the 20B side. Further, the connecting portion between the top surface opposite end 20B and the side surface 20S has a smaller diameter DP1 on the top surface opposite end 20B side than the diameter DP2 of the side surface 20S on the piston top surface 20T side than this connecting portion. As shown in FIG.

  At the connection portion between the piston top surface 20T and the side surface 20S, the diameter of the piston 20 changes from DP1 to DP2 from the piston top surface 20T toward the top surface opposite end 20B. A connecting portion between the piston top surface 20T and the side surface 20S is referred to as a top surface side piston diameter changing portion GT1. Further, at the connecting portion between the top surface opposite end 20B and the side surface 20S, the diameter of the piston 20 changes from DP1 to DP2 from the top surface opposite end 20B toward the piston top surface 20T. The connecting portion between the top surface opposite end 20B and the side surface 20S is referred to as a top surface opposite piston diameter changing portion GT2.

  The piston 20 is provided with an annular member (top surface side annular member) 40T in a stepped shape on the piston top surface 20T side, and an annular member is formed in a stepped shape on the top surface opposite end 20B side. (A top surface opposite side annular member) 40B is provided. When the top surface side annular member 40T and the top surface opposite side annular member 40B are not distinguished, they are simply referred to as the annular member 40. The annular member 40 is provided at at least one end of a region where the gas bearing GB is formed in the reciprocating direction of the piston 20. In the present embodiment, the annular member 40 is provided at both ends of the region where the gas bearing GB is formed in the reciprocating direction of the piston 20.

  When the annular member 40 is provided at one end of the region where the gas bearing GB is formed in the reciprocating direction of the piston 20, it is preferably provided on the piston top surface 20T side. Since the piston top surface 20T is always in contact with the working fluid in the working fluid space MS, foreign matter may enter between the piston 20 and the cylinder 30 from the piston top surface 20T side than the top surface opposite end 20B. Because it becomes higher. Thus, by providing the annular member 40 at least on the piston top surface 20T side in the both ends of the region where the gas bearing GB is formed, the possibility that foreign matter may enter between the piston 20 and the cylinder 30 can be reduced.

  As shown in FIG. 6, the annular member 40 is an annular and endless member. The annular member 40 is attached to the piston 20 by, for example, adhesion or welding. Further, the annular member 40 may be fitted into the piston 20 by making the inner diameter of the annular member 40 smaller than the outer diameter of the portion of the piston 20 to which the annular member 40 is attached. The hardness of the annular member 40 is set lower than the hardness of the inner surface 30 </ b> S of the cylinder 30. As a result, when a foreign object tries to bite into the inner surface 30S of the cylinder 30, the foreign object bites into the annular member 40 having a lower hardness than the inner surface 30S of the cylinder 30, so that the inner surface 30S of the cylinder 30 may be damaged by the foreign object. Can be reduced.

  The hardness of the annular member 40 is preferably 1/10 or less of the hardness of the inner surface 30S of the cylinder 30. In this way, since the annular member 40 can capture the foreign material more reliably, the risk of damaging the inner surface 30S of the cylinder 30 is further reduced. As a material constituting the annular member 40, a heat-resistant resin material can be used. As such a material, for example, a polyamide-based resin or an aramid resin can be used.

  The gas bearing GB is formed between the piston 20 and the cylinder 30. The region where the gas bearing GB is formed in the reciprocating motion direction of the piston 20 is the top surface side piston diameter changing portion GT1 and the top surface opposite piston. Between the diameter change part GT2. Accordingly, the top surface side piston diameter changing portion GT1 and the top surface opposite side piston diameter changing portion GT2 are the respective end portions of the region where the gas bearing GB is formed in the reciprocating motion direction of the piston 20.

  As will be described later, the outer peripheral surface 40S of the annular member 40 and the side surface 20S of the piston 20 are formed to be substantially the same, so that the function of the gas bearing GB is substantially achieved even at the portion where the annular member 40 is disposed. It is thought that can be demonstrated. However, for example, the clearance between the annular member 40 and the cylinder 30 has changed due to progress of wear of the annular member 40, loss of a part of the annular member 40, or trapping by the foreign material biting into the annular member 40. In this case, it is conceivable that the function of the gas bearing GB cannot be sufficiently exhibited.

  Even in such a case, the area between the top surface side piston diameter changing portion GT1 and the top surface opposite side piston diameter changing portion GT2 is an area where the clearance between the piston 20 and the cylinder 30 does not change. In the present embodiment, this region is handled as a region where the gas bearing GB is formed in the reciprocating direction of the piston 20. That is, in a state where the annular member 40 is removed from the piston 20, an area in which the clearance between the piston 20 and the cylinder 30 is a dimension set in advance to form the gas bearing GB is gas in the reciprocating direction of the piston 20. It is handled as a region where the bearing GB is formed.

  The distance from the piston top face 20T to the top face side piston diameter changing portion GT1 in the reciprocating direction of the piston 20 is L1, and the top face opposite piston diameter change from the top face opposite end 20B in the reciprocating direction of the piston 20 is L1. The distance to the part GT2 is L2. The distance L1 is the thickness of the top surface side annular member 40T, and the distance L2 is the thickness of the top surface opposite side annular member 40B. Here, the thickness of the annular member 40 is a dimension of the annular member 40 in a direction parallel to the central axis (annular member central axis) Zr (FIGS. 5 and 6) of the annular member 40. When the annular member 40 is attached to the piston 20, the annular member central axis Zr and the piston central axis Zp coincide with each other.

  In the present embodiment, the thickness L1 of the top surface side annular member 40T and the thickness L2 of the top surface opposite side annular member 40B are the same size, but both may differ depending on the specifications of the Stirling engine 100. Good. The thickness of the top surface side annular member 40T and the top surface opposite side annular member 40B, that is, the thickness of the annular member 40 is 10 times or more the designed value of the clearance of the gas bearing GB, that is, the clearance tc between the piston 20 and the cylinder 30. It is preferable to make it 100 times or less. In this way, it is possible to reliably capture the foreign material that is about to enter the clearance tc between the piston 20 and the cylinder 30 by causing the foreign material to bite into the annular member 40, and to prevent the captured foreign material from falling off. Moreover, if it does in this way, the reduction | decrease of the area | region in which the gas bearing GB is formed by providing the annular member 40 can be suppressed.

  When the outer diameter of the annular member 40 is DR1 and the inner diameter is DR2, the dimension in the radial direction (referred to as radial thickness) of the annular member 40 is (DR1-DR2) / 2 (see FIG. 6). The radial thickness of the annular member 40 is preferably 10 times or more the design value of the clearance tc between the piston 20 and the cylinder 30. In this way, it is possible to reliably capture the foreign material that is about to enter the clearance tc between the piston 20 and the cylinder 30 by causing the foreign material to bite into the annular member 40, and to prevent the captured foreign material from falling off.

  As shown in FIG. 7A, in a state where the annular member 40 is attached to the piston 20, the outer peripheral surface 40 </ b> S of the annular member 40 is at least the same (same surface) as the side surface 20 </ b> S of the piston 20. In this case, the distance tcr between the cylinder 30 and the annular member 40 is equal to the clearance tc between the cylinder 30 and the piston 20. Here, the clearance tc between the cylinder 30 and the piston 20 is a distance between the piston 20 and the cylinder 30 in a portion where the annular member 40 is not attached, and the cylinder 30 and the piston 20 in the region where the gas bearing GB is formed. Clearance tc.

  In the present embodiment, the distance tcr between the cylinder 30 and the annular member 40 shown in FIG. 7 is set to be equal to or less than the clearance tc between the cylinder 30 and the piston 20. In this way, by setting the distance tcr between the cylinder 30 and the annular member 40 to be equal to or less than the clearance tc between the cylinder 30 and the piston 20, the foreign member is more reliably removed from the end of the region where the gas bearing GB is formed. 40 can be captured. As a result, entry of foreign matter into the clearance tc between the cylinder 30 and the piston 20 can be suppressed, and a decrease in durability of the piston 20 and the cylinder 30 can be suppressed, and the function of the gas bearing GB can be surely exhibited. .

  FIG. 8 is an enlarged view showing another configuration example of the piston and the cylinder included in the Stirling engine according to the present embodiment. Since the piston top surface 20T of the high temperature side piston 20H shown in FIG. 1 is in contact with the high temperature working fluid heated by the heater 105, it thermally expands. In the Stirling engine 100 shown in FIG. 1, since the gas bearing GB is interposed between the piston 20 and the cylinder 30, the clearance tc between them is set as small as several μm to several tens of μm. For this reason, when the piston 20 is thermally expanded in the radial direction, the piston 20 and the cylinder 30 may come into contact with each other.

  The piston 20 shown in FIG. 8 has a diameter DP1 of the piston 20 in a range of a distance L0 from the piston top surface 20T to a predetermined portion (ie, top surface side piston diameter changing portion GT1) from the top surface opposite end 20B. , Smaller than the diameter DP2 of the piston 20 in the range from the position of the distance L0 to the top surface opposite end 20B. As a result, a portion where the clearance tl between the piston 20 and the cylinder 30 is formed larger than the clearance tc between the piston 20 and the cylinder 30 in the region where the gas bearing GB is formed on the piston top surface 20T side (clearance expanding portion). ) Is formed. Due to the clearance expansion portion formed on the piston top surface 20T side, the piston 20 is prevented from contacting the piston 20 and the cylinder 30 due to thermal expansion in the radial direction of the piston 20 itself.

  Here, the portion where the diameter of the piston 20 changes on the piston top surface 20T side is referred to as a top surface side piston diameter changing portion GT1. The piston 20 shown in FIG. 8 is the same as the piston 20 shown in FIG. 4 described above, but the distance L0 to the top surface side piston diameter changing portion GT1 is made larger than the thickness L1 of the top surface side annular member 40T. It is. Thus, when the top surface side annular member 40T is attached to the piston 20, the clearance tl between the piston 20 and the cylinder 30 on the piston top surface 20T side is such that the piston 20 and the cylinder 30 in the region where the gas bearing GB is formed. It becomes larger than clearance tc.

  In the piston 20 (FIG. 8) having the clearance enlarged portion on the piston top surface 20T side, the region where the gas bearing GB is formed in the reciprocating motion direction of the piston 20 is the top surface side piston as in the piston 20 shown in FIG. Between the diameter changing portion GT1 and the top surface opposite piston diameter changing portion GT2. Accordingly, the top surface side piston diameter changing portion GT1 and the top surface opposite side piston diameter changing portion GT2 are the respective end portions of the region where the gas bearing GB is formed in the reciprocating motion direction of the piston 20.

  The piston 20 has a top surface side piston diameter that is a boundary between the clearance increasing portion and the region where the gas bearing GB is formed, that is, one end of the region where the gas bearing GB is formed in the reciprocating direction of the piston 20. A top surface side annular member 40T is provided in the change part GT1. In the piston 20, the top surface opposite side annular member 40 </ b> B is also provided on the top surface opposite side piston diameter changing part GT <b> 2 which is the other end of the region where the gas bearing GB is formed in the reciprocating direction of the piston 20. As described above, the annular member 40 only needs to be provided at at least one end of the region where the gas bearing GB is formed in the reciprocating direction of the piston 20.

  FIG. 9 is an enlarged view of a piston and a cylinder included in a Stirling engine according to a modification of the present embodiment. FIG. 10A is a perspective view of an annular member included in a Stirling engine according to a modification of the present embodiment. FIG. 10-2 is a partial side view of the annular member included in the Stirling engine according to the modification of the present embodiment. FIGS. 11A and 11B are plan views of an annular member provided in a Stirling engine according to a modification of the present embodiment. FIG. 12 is an enlarged view of a portion where an annular member is attached to a piston included in a Stirling engine according to a modification of the present embodiment.

  In the piston 20a of this modification, an annular member mounting groove 26 for attaching the annular member 40a is formed on the piston top surface 20T side. The annular member mounting groove 26 is formed toward the circumferential direction of the piston 20a. A region indicated by AGB from the top surface opposite end 20B side to the top surface opposite end 20B of the annular member mounting groove 26 is a region where the gas bearing GB is formed.

  As shown in FIG. 10A, the annular member 40 a attached to the annular member attachment groove 26 is an annular and end member having an abutment 42. In the annular member 40a shown in FIG. 10A, the ends of the annular member 40a at the joint 42 are separated from each other. FIG. 11A is a state before the piston 20a to which the annular member 40a is attached is assembled into the cylinder 30. The free shape of the annular member 40a (open shape, and the state in which the annular member 40a is removed from the piston 20a) ). In the present modification, the outer diameter DR1_b of the annular member 40a is formed larger than the inner diameter DC2 of the cylinder 30 shown in FIG.

  FIG. 11-2 shows a state after the piston 20a to which the annular member 40a is attached is assembled into the cylinder 30, and the outer diameter DR1_a of the annular member 40a at this time is equal to the inner diameter DC2 of the cylinder 30 shown in FIG. Become. That is, when the piston 20a to which the annular member 40a is attached is assembled into the cylinder 30, the outer peripheral surface 40Sa of the annular member 40a and the inner surface 30S of the cylinder 30 come into contact as shown in FIG. Thereby, in this modification, the foreign material which is going to enter between the piston 20a and the cylinder 30 can be reliably captured by the annular member 40a. When the annular member 40a comes into contact with the cylinder 30, the material, shape, and dimensions of the annular member 40a are adjusted so that the friction between the annular member 40a and the cylinder 30 comes into contact with each other. .

  In addition, you may comprise the annular member 40a so that the edge parts of the annular member 40a in the abutment 42 may contact | connect. In this case, when the annular member 40a is attached to the piston 20a, the outer peripheral surface 40Sa of the annular member 40a is set to be the same as the side surface 20S of the piston 20a or the inner surface 30S side of the cylinder 30. As a result, the foreign material that is about to enter between the piston 20a and the cylinder 30 is captured by the annular member 40a.

  As shown in FIGS. 9, 10-1, and 10-2, a plurality of grooves (annular member grooves) 41 are formed on the outer peripheral surface 40Sa of the annular member 40a. The annular member groove 41 is formed in a direction intersecting with the direction in which the piston 20a reciprocates (the direction of the arrow U in FIG. 9 and the direction parallel to the piston central axis Zp), and in the direction in which the piston 20a reciprocates. The end portions 43 and 43 of the annular member 40a are passed through.

  As shown in FIG. 12, when the piston 20a moves in the direction of the top dead center, that is, moves in the direction of reducing the volume of the working fluid space MS, the pressure P1 on the working fluid space MS side than the annular member 40a is It becomes higher than the pressure P2 on the opposite side to the working fluid space MS with respect to the annular member 40a. A pressure difference (P1-P2) is generated between the working fluid space MS side and the opposite side of the working fluid space MS with the annular member 40a as a boundary, whereby the inner peripheral surface 40ai of the annular member 40a becomes the inner surface 30S of the cylinder 30. Receive the power to head. As a result, the outer peripheral surface 40Sa of the annular member 40a is pressed against the inner surface 30S of the cylinder 30. As a result, there is a possibility that friction between the annular member 40a and the cylinder 30 may increase, or pressure deviation may occur in the gas bearing GB.

  For this reason, in this modification, the annular member groove 41 is provided on the outer peripheral surface 40Sa of the annular member 40a, and the pressure on the working fluid space MS side and the pressure in the working fluid space MS are made equal to the annular member 40a. Thereby, the bias of the pressure of the gas bearing GB is suppressed, the function of the gas bearing GB is reliably exhibited, and the friction between the annular member 40a and the cylinder 30 is reduced. Further, since the rigidity of the annular member 40a is reduced by providing the annular member groove 41, the force with which the annular member 40a is pressed against the cylinder 30 can be reduced, and the friction between the annular member 40a and the cylinder 30 can be reduced.

  The annular member grooves 41 are preferably provided at equal intervals in the circumferential direction of the annular member 40a. If it does in this way, the nonuniformity of the pressure in the circumferential direction of the annular member 40a can be suppressed. Further, the function of the annular member groove 41 may be exhibited at the joint 42 of the annular member 40a. As described above, the annular member groove 41 is formed in a direction that intersects the direction in which the piston 20a reciprocates. As a result, foreign substances are prevented from entering the region where the gas bearing GB is formed through the annular member groove 41 from the working fluid space MS side shown in FIG.

  As shown in FIG. 10-2, the inclination angle of the annular member groove 41 with respect to the piston central axis Zp (the smaller one of the angles formed by the piston central axis Zp and the annular member groove 41) θ should be 30 degrees or more. Preferably, it is 45 degrees or more. If the inclination angle θ is increased, it becomes difficult to form the annular member groove 41 in the annular member 40a. Therefore, the inclination angle θ is preferably 30 degrees or less.

  FIG. 13A is a partial side view illustrating another configuration example of the annular member included in the Stirling engine according to the modification of the present embodiment. You may make it provide the V-shaped annular member groove | channel 41a like the annular member 40a1 shown to FIGS. In this way, it is possible to more effectively suppress foreign substances from entering the region where the gas bearing GB is formed through the annular member groove 41a from the working fluid space MS side shown in FIG. The inclination angles of the V-shaped annular member groove 41a are θ1 and θ2, but θ1 and θ2 may be different, or both may be the same size.

  FIG. 13-2 is a partial side view showing another configuration example of the joint having the annular member included in the Stirling engine according to the modification of the present embodiment. Like the annular member 40a2 shown in FIG. 13-2, the joint 42a may be V-shaped. Accordingly, it is possible to effectively suppress foreign matters from entering the region where the gas bearing GB is formed through the joint 42a.

  FIG. 14 is a schematic diagram illustrating a configuration example when the Stirling engine according to the present embodiment is used for exhaust heat recovery of an internal combustion engine. In the present embodiment, the output of the Stirling engine 100 is input to the internal combustion engine transmission 4 via the Stirling engine transmission 5 and is combined with the output of the internal combustion engine 1 to be taken out.

  In the present embodiment, the internal combustion engine 1 is mounted on a vehicle such as a passenger car or a truck, and serves as a power source for the vehicle. The internal combustion engine 1 generates an output as a main power source while the vehicle is running. On the other hand, the Stirling engine 100 cannot produce the minimum necessary output unless the temperature of the exhaust gas Ex reaches a certain level. Therefore, in the present embodiment, the Stirling engine 100 collects thermal energy from the exhaust gas Ex of the internal combustion engine 1 to generate an output when the temperature of the exhaust gas Ex discharged from the internal combustion engine 1 exceeds a predetermined temperature. Drive the vehicle. Thus, the Stirling engine 100 is a power source that the vehicle follows.

  The heater 105 provided in the Stirling engine 100 is disposed in the exhaust passage 2 of the internal combustion engine 1. A regenerator (see FIG. 1) 106 of the Stirling engine 100 may be disposed in the exhaust passage 2. The heater 105 provided in the Stirling engine 100 is provided in a hollow heater case 3 provided in the exhaust passage 2.

  In the present embodiment, the thermal energy of the exhaust gas Ex recovered using the Stirling engine 100 is converted into kinetic energy by the Stirling engine 100. A crank shaft 110 that is an output shaft of the Stirling engine 100 is attached with a clutch 6 that is a power interrupting means, and the output of the Stirling engine 100 is transmitted to the Stirling engine transmission 5 via the clutch 6.

  The output of the internal combustion engine 1 is input to the internal combustion engine transmission 4 via the output shaft 1 s of the internal combustion engine 1. The internal combustion engine transmission 4 synthesizes the output of the internal combustion engine 1 and the output of the Stirling engine 100 output from the Stirling engine transmission 5 and outputs the resultant to the transmission output shaft 9. The drive wheel 11 is driven via

  Here, the clutch 6 serving as the power interrupting means is provided between the internal combustion engine transmission 4 and the Stirling engine 100. In this embodiment, it is provided between the input shaft 5 s of the Stirling engine transmission 5 and the crankshaft 110 of the Stirling engine 100. The clutch 6 engages and disengages, thereby interrupting mechanical connection between the crankshaft 110 of the Stirling engine 100 and the input shaft 5s of the Stirling engine transmission 5. Here, the clutch 6 is controlled by the engine ECU 50.

  Since the Stirling engine 100 recovers the thermal energy of the exhaust gas Ex discharged from the internal combustion engine 1, when the temperature of the exhaust gas Ex is low, such as when the internal combustion engine 1 is cold started, the thermal energy is recovered from the exhaust gas Ex. Cannot generate output. Therefore, the clutch 6 is released until the Stirling engine 100 can generate output, the Stirling engine 100 and the internal combustion engine 1 are disconnected, and the energy loss due to the Stirling engine 100 being driven by the internal combustion engine 1 is lost. Suppress.

  When the clutch 6 is engaged, the crankshaft 110 of the Stirling engine 100 and the output shaft 1 s of the internal combustion engine 1 are directly connected via the Stirling engine transmission 5 and the internal combustion engine transmission 4. As a result, the output generated by the Stirling engine 100 and the output generated by the internal combustion engine 1 are combined by the internal combustion engine transmission 4 and taken out from the transmission output shaft 9. On the other hand, when the clutch 6 is released, the output shaft 1s of the internal combustion engine 1 is separated from the crankshaft 110 of the Stirling engine 100 and rotates.

  The piston provided in the Stirling engine 100 of the present embodiment shown in FIG. 12 prevents foreign matter from entering between the piston and the cylinder by the annular member provided on the piston, thereby suppressing a decrease in the durability of the piston and the cylinder. Therefore, stable operation can be realized. Further, in the Stirling engine 100 according to the present embodiment, foreign matters hardly enter between the piston and the cylinder by the annular member provided on the piston.

  As a result, even if the Stirling engine 100 mounted on the vehicle receives vibration and the clearance between the piston and the cylinder changes, it can be avoided that the durability of the piston or the cylinder is deteriorated due to foreign matter between the piston and the cylinder. . Thus, when the Stirling engine 100 according to the present embodiment is used for exhaust heat recovery of the internal combustion engine 1 mounted on a vehicle, exhaust heat can be recovered stably and sufficient durability can be ensured.

  As described above, in the present embodiment, a gas bearing is interposed between the piston and the cylinder, and at least one end of a region where the gas bearing is formed in the reciprocating direction of the piston is an annular member having a hardness lower than that of the cylinder. Is provided. With such a configuration, a foreign material that is about to enter between the piston and the cylinder is caught in the annular member and captured. As a result, entry of foreign matter between the piston and the cylinder can be suppressed, and a decrease in durability of the piston or cylinder can be suppressed. In addition, since foreign matter can be prevented from entering between the piston and the cylinder, the load bearing capability of the gas bearing can be reliably exhibited, and lubrication between the piston and the cylinder can be ensured. As a result, the reliability of the piston engine is improved.

  In addition, when dust or burrs of parts that could not be removed by cleaning are mixed into the working fluid, or when the piston engine is a Stirling engine, foreign matter from components of the heat exchanger exposed to high temperatures is activated. It may be mixed into the fluid. According to the configuration of the present embodiment, such a foreign matter can be reliably removed by the annular member provided on the piston, so that the penetration of the foreign matter between the piston and the cylinder is suppressed, and the durability of the piston or the cylinder is reduced. Reduction can be suppressed.

  As described above, the piston engine and the Stirling engine according to the present invention are useful for a piston engine that does not use a piston ring. In particular, gas flows out from a pressure accumulation space formed in the piston between the piston and the cylinder. Suitable for piston engines that make up gas bearings.

It is sectional drawing which shows the structure of the Stirling engine which is a piston engine which concerns on this embodiment. It is a top view which shows the gas bearing with which the Stirling engine which concerns on this embodiment is provided. It is explanatory drawing which shows the structural example of the gas bearing with which the Stirling engine which concerns on this embodiment is provided, and the support structure of a piston. It is explanatory drawing which shows the structural example of the gas bearing with which the Stirling engine which concerns on the modification of this embodiment is provided, and the support structure of a piston. It is an enlarged view of the piston and cylinder with which the Stirling engine which concerns on this embodiment is provided. It is a perspective view of the cyclic | annular member provided in the piston of the Stirling engine which concerns on this embodiment. It is a top view of the cyclic | annular member provided in the piston of the Stirling engine which concerns on this embodiment. It is an enlarged view of the part where an annular member is attached to the piston with which the Stirling engine concerning this embodiment is provided. It is an enlarged view which shows the other structural example of the piston and cylinder with which the Stirling engine which concerns on this embodiment is provided. It is an enlarged view of the piston and cylinder with which the Stirling engine which concerns on the modification of this embodiment is provided. It is a perspective view of the annular member with which the Stirling engine which concerns on the modification of this embodiment is provided. It is a partial side view of the annular member with which the Stirling engine which concerns on the modification of this embodiment is provided. It is a top view of the annular member with which the Stirling engine which concerns on the modification of this embodiment is provided. It is a top view of the annular member with which the Stirling engine which concerns on the modification of this embodiment is provided. It is an enlarged view of the part by which an annular member is attached to the piston with which the Stirling engine which concerns on the modification of this embodiment is provided. It is a partial side view which shows the other structural example of the annular member with which the Stirling engine which concerns on the modification of this embodiment is provided. It is a partial side view which shows the other structural example of the joint which the annular member with which the Stirling engine which concerns on the modification of this embodiment has is provided. It is a mimetic diagram showing the example of composition in the case of using the Stirling engine concerning this embodiment for exhaust heat recovery of an internal-combustion engine.

Explanation of symbols

20, 20a Piston 20B Top surface opposite end 20Bp Bottom 20T Piston top surface 20S Side surface 20Sp Side portion 20T Top surface 20Tp Top portion 26 Annular member mounting groove 30 Cylinder 30S Inner surface 40, 40a, 40a1, 40a2 Annular member 40ai Inner circumferential surface 40Si , 40Sa outer peripheral surface 40B top surface opposite side annular member 40T top surface side annular member 41, 41a annular member groove 42, 42a abutment 43 end 60 approximate linear mechanism 100, 100a Stirling engine GB gas bearing GT1 top side piston diameter changing part GT2 Piston diameter changing part on the opposite side of the top surface

Claims (8)

A piston that reciprocates in the cylinder;
A gas bearing formed between the piston and the cylinder;
An annular member having a lower hardness than the inner surface of the cylinder, provided at at least one end of a region where the gas bearing is formed in the reciprocating direction of the piston;
A piston engine comprising: The piston is
A gas reservoir surrounded by an outer shell of the piston and storing gas;
A plurality of air holes provided on the side of the piston, and the gas bearing is formed by allowing the gas inside the gas reservoir to flow out between the piston and the cylinder;
A piston engine characterized by comprising:   The piston engine according to claim 1, wherein the annular member is provided at least on a top surface side of the piston. The piston is formed such that the diameter of a predetermined portion from the top surface of the piston toward the end opposite to the top surface is smaller than the diameter of the portion where the gas bearing is formed, and the clearance between the cylinder and the piston Has a clearance expansion portion formed larger than the portion where the gas bearing is formed,
4. The piston engine according to claim 3, wherein the annular member is provided at a portion where a diameter of the piston changes on a top surface side of the piston.   5. The piston engine according to claim 1, wherein an outer peripheral surface of the annular member is the same as a side surface of the piston or is closer to an inner surface side of the cylinder than a side surface of the piston. .   The piston engine according to any one of claims 1 to 3, wherein the annular member is an end member having a joint, and a free-form diameter is larger than an inner diameter of the cylinder. .   The outer circumferential surface of the annular member is provided with a groove penetrating the ends of the annular member in the direction intersecting with the direction in which the piston reciprocates and in the direction in which the piston reciprocates. The piston engine according to claim 6. A heat exchanger comprising: a heater that heats the working fluid; a regenerator that is connected to the heater and through which the working fluid passes; and a cooler that is connected to the regenerator and cools the working fluid. When,
A cylinder into which the working fluid that has passed through the heat exchanger flows in and out;
A piston that reciprocates in the cylinder;
A gas bearing formed between the piston and the cylinder;
An annular member having a lower hardness than the inner surface of the cylinder, provided at at least one end of a region where the gas bearing is formed in the reciprocating direction of the piston;
An approximate linear mechanism that supports the piston and moves the piston approximately linearly;
A Stirling engine comprising:

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